1. Field of the Invention
The present invention relates to a generator-brake integration type rotating machine, and more particularly, to a generator-brake integration type rotating machine which can obtain braking force using electricity generated by external rotational kinetic energy.
2. Description of the Related Art
In general, in devices requiring braking force, the following factors should be considered. First, the braking force must have no ripple. Second, the same braking force should be obtained under the same set values. Third, the devices must have inertia force. Fourth, braking should be performed in a silent manner.
Meanwhile, devices for obtaining braking force through mechanical friction between two objects moving relative to each other have problems as described below. That is to say, frictional heat is generated, frictional surfaces are unevenly worn, and braking force is changed due to the alteration of physical properties.
In order to cope with these problems, recently, research has been conducted for devices which can generate braking force using eddy current. In this case of using eddy current, the problems in relation to ripple, wear, noise, etc. can be solved. However, since braking force generated by eddy current is nonlinear in relation to current, speed, temperature, physical properties, etc., it is difficult to control the braking force.
For this reason, the devices for generating braking force using eddy current are currently being adopted for simple application.
For example, the brake device with a combination of power-generating and eddy-current magnetic resistance disclosed in U.S. Pat. No. 6,084,325 has a disk which rotates, a brake yoke which is disposed outside the disk, and a generator which is disposed inside the disk, such that braking force can be provided through self-generation without using an external power source.
Nevertheless, in the brake device with a combination of power-generating and eddy-current magnetic resistance disclosed in U.S. Pat. No. 6,084,325, a solenoid for generating eddy current is disposed outside the disk, and the generator is disposed inside the disk. In this case, while braking force can be maximized, an air gap is likely to be changed due to machining errors and assembly errors. Also, since magnets are attached to the heat generating section of the disk, the characteristics of the magnets are apt to be deteriorated with the lapse of time. Therefore, a disadvantage is caused in that the size of the magnets increases in order to suppress the change in the characteristics of the magnets by heat. Further, because inertia compensation is not conducted in the brake device, another disadvantage is caused in that the size of the disk markedly increases. Moreover, due to the fact that only one solenoid is used so as to obtain sufficient torque, the temperature of the heat generated in coils may be excessively increased, and it is difficult to constantly control torque because of current change due to a rise in the temperature of the coils. In addition, since a solenoid yoke is disposed at one side, force is concentratedly applied to one side. Therefore, the functionality of a bearing, which supports a shaft, may be degraded, and the available service life of the bearing can be shortened.
For another example, an autonomous generation brake assembly disclosed in U.S. Pat. No. 6,581,731 has a solenoid yoke, in which a solenoid for a brake and a solenoid for a generator are integrated with each other, in a core. Since the autonomous generation brake assembly is a core integration type, errors can be reduced in the fabrication procedure thereof. However, the solenoids of the brake and the generator are not positioned at regular angular intervals in the circumferential direction. Due to this fact, a number of magnets are needed for the generation of electricity, and torque ripple increases during the generation of electricity. Further, because the solenoid for the brake is positioned inside the yoke, the magnitude of braking torque by eddy current considerably decreases. Hence, in order to prevent the braking torque from decreasing, coils having a large number of turns are needed.
For further example, in the magnetic controlled loading device in combination of a power generating set and an adjusting drive mechanism disclosed in U.S. Pat. No. 7,018,324, the amount of eddy current generated in a metal conductor increases as the distance between the metal conductor and permanent magnets is shortened, and therefore, braking force can be increased. The device employs compression springs to push a magnetic plate toward a flywheel.
Nonetheless, since the elasticity of the compression springs changes with the lapse of time, the air gap between the metal conductor and the permanent magnets during a single rotation of a motor may vary, whereby the braking force can be changed. In addition, because the length of the air gap and the magnitude of braking torque have a nonlinear relationship, a drawback is caused in that it is difficult to control a brake.